textproduct: Rapid City

KEY MESSAGES

- Upslope-enhanced snowfall for the northern/Wyoming Black Hills through early Wednesday - Thursday through early next week, northwest flow aloft will push a series of disturbances through the region bringing periodic chances for light precipitation

DISCUSSION

(Today Through Monday) Issued at 131 AM MST Tue Dec 2 2025

08z surface analysis had low over central SK with a warm front into western NE, just about through the far eastern reaches of the CWA. Water vapour loop had upper trough over western Canada into the Pacific northwest with 140kt jet streak zipping over the western BC coast. Lead shortwave energy over MT/ID creating some light radar returns, some of which area starting to brighten as they hit the higher elevations of the northern/Wyoming Black Hills. Upper trough and upslope the the main forecast concerns in the short term.

Today/tonight, upper trough moves southeast with the main pieces of energy passing well to our southwest and to our northeast. Synoptic forcing rather light with weak QG-forcing/low level frontogenesis. Canadian surface low will drag a cold front through the area later today/tonight, which will focus the main QPF chances for the plains. Not expecting much QPF on the plains with rain mixing in east of the Black Hills ahead of the cold front, quickly changing to snow behind it. The main story will be the upslope enhancement for the northern/Wyoming Black Hills. Froude numbers already above 1 early this morning with increasing 0-2km RH today, becoming saturated tonight. Forecast soundings suggest the best upward vertical motion will be in the dendritic growth zone tonight, which will fluff up the snow. Latest HREF LPMM 24-hour QPF gives about 0.50" liquid equivalent precipitation by Wednesday morning. HREF probabilistic depictions show 70-100% chance >0.25" QPF and 50% chance 0.50" QPF. Subjective pattern recognition and high resolution deterministic model output suggest these values reasonable. Will hoist a Winter Weather Advisory for the northern/Wyoming Black Hills to account. Considered putting headlines up for northern Campbell/Crook County Plains, but not coming up with enough snow/impacts to issue at this time. Isallobaric forcing behind the cold front supports breezy/locally windy spots. Temperatures will be near guidance.

Wednesday will 10-20F colder than today with a bit of snap in the air per northwest winds averaging 12-22 mph. Upslope snow should quickly wane in the morning.

The rest of the forecast looks unsettled as northwest flow aloft propels a series of disturbances through the northern Plains. We'll be on the edge of the warmer air initially, but the latest ensemble guidance shows a slow warming trend into early next week, albeit with increasing temperature spreads. Best chance of accumulating snow will continue to be over the northern Black Hills given expected boundary layer flow regime.

AVIATION

(For the 18Z TAFS Through 18Z Wednesday) Issued At 1027 AM MST Tue Dec 2 2025

Areas of MVFR ceilings with light rain and snow will continue across much of the area this afternoon. More widespread precipitation chances overspread the area late this afternoon from west to east with widespread MVFR/IFR conditions developing, persisting into the overnight hours. LIFR conditions will occur over the higher elevations of the Black Hills tonight. Conditions will slowly improve from west to east by late Wednesday morning.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Winter Weather Advisory until 6 AM MST Wednesday for SDZ024. WY...Winter Weather Advisory until 6 AM MST Wednesday for WYZ057.